Today was my first time trying this commute during the week. I've done it a handful of times on weekends. I left at 6:35 am, and arrived at work at 7:30 am. Everything was basically the same, in fact Dot Ave and Mass Ave had lighter traffic than they do on a Saturday afternoon. However, Granite Ave through Milton was frightening. The stretch from Squantum street until the 93 on ramp was like a hornets nest. Next time I do this, which will probably be this Friday, I'm going to try either the NPR bridge (sidewalk) into Boston or Adams St in Milton. I have done both before and don't like either one for various reason, but they're definitely both safer during rush hour.
As a tip to others, I would say Granite Ave is the best way to get from Quincy to Boston via bike, as long as you're going off peak driving hours. Otherwise it is pretty scary. The funny thing is traffic on 93 gets so backed up that the entire on ramp on Granite Ave is like a parking lot. So people are just speeding past me for a few hundred yards to go wait in line. Funny how they're willing to possibly threaten another person's life for the privilege of not having to slow down a few hundred yards earlier.